Mary-Kate & Ashley Olsen's Younger Sister Hits Sundance

Mary-Kate and Ashley Olsen's sister Elizabeth has moved past her earlier work in projects such as The Adventures of Mary-Kate & Ashley: The Case of Thorn Mansion. Way past it.

In fact, the 21-year-old actress's two new films set to premiere at the Sundance Film Festival in Park City, Utah, are dark and gritty, tackling topics such as cults and sexual abuse.

Elizabeth's earlier roles in her sister's films were significantly less taxing. "Sometimes I had lines, and sometimes I'd just sit on a stool," she tells PEOPLE, laughing. "I couldn't pronounce my r's."

After studying acting in high school and then attending New York University's Tisch Schol of the Arts, Olsen, who is three years younger than Mary-Kate and Ashley, quickly landed work in independent films, including the duo of films premiering at Sundance, Silent House and Martha Marcy May Marlene, which both garnered her praise.

Olsen insists that working on these darker projects wasn't calculated to distinguish herself from her earlier, kid-friendly fare.

"I wasn't trying to shape any beginnings of a career," she says. "You can't guess how things are going to go."